"In preparation for this audit, VHA (Veterans Health Administration) Central Office learned on May 12 that a Durham VA Medical Center employee indicated that some employees at that facility may have engaged in inappropriate scheduling practices at some point between 2009 and 2012," the Monday statement read.

"VA takes any allegations about patient care or employee misconduct very seriously. If the allegations are true, the inappropriate behavior is unacceptable and employees will be held accountable."

A VA scheduler in San Antonio said clerks scheduling medical appointments for veterans were "cooking the books" at their bosses' behest to hide the fact some had to wait weeks, if not months, for appointments.

The VA's official policy is that all patients should be able to see a doctor, dentist or some other medical professional within 14 days of their requested/preferred date. Any wait longer than two weeks is supposed to documented. But many veterans end up waiting longer, and the delays are never reported, veterans and their advocates say.

Shinseki has been subpoenaed by the House Veterans' Affairs Committee.

CNN has submitted numerous requests for an interview with Shinseki; the secretary has refused them all.